Add autocomplete feature

[arpit-saxena]

The user enters some letters and the program returns all the words with the prefix

Eg: ble would give bleed, bless, blessing, blessed, etc.

It would be good to give the suggestions as soon as the person types the letters, and it wouldn't take much time considering how all the words are stored in the dictionary

Support for backspace key would be nice but not fast enough because the tree is not doubly linked. We could consider making it doubly linked, or maybe storing the pointers to the letters that user had entered in a stack. Backspace results in popping the top pointer.